Location of cooperative tags with personal electronic device

ABSTRACT

The present disclosure relates to location and communication systems that can be utilized for locating people, pets and other objects with a software defined radio set. A personal electronic device (PED) such as a cellular telephone, personal data assistant (PDA) or other device that include a software defined radio set can be configured for operation as a locator device. The PED transmits a signal A transponder or micro-transponder (MT) that is tagged to an object is arranged to reply to a transmission received from the PED. The PED based locator is arranged to calculate a distance between the PED and the MT using the time-of-flight (TOF) between the transmission and the receipt of a reply. The absolute geographic position of the PED can be determined using satellite navigation information, while the position of the MT relative to the PED can be determined from the TOF information.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/549,478, filed Nov. 20, 2014, which is a divisional of U.S. patentapplication Ser. No. 13/049,599, filed Mar. 16, 2011, now U.S. Pat. No.8,583,145, which is a divisional of U.S. patent application Ser. No.11/924,553, filed Oct. 25, 2007, now U.S. Pat. No. 7,917,155, whichclaims priority to U.S. Provisional Patent Application Ser. No.60/854,827, filed Oct. 27, 2006. The entire content of all of which areincorporated by reference.

FIELD OF THE INVENTION

The present disclosure relates generally to location and communicationsystems for locating people, pets, and other objects. More particularlythe disclosure relates to the use of portable devices such as cellulartelephones, PDAs and other personal electronic devices that includesoftware definable radio sets. A software application program can beused to configure the software defined radio for use in locating peopleand/or objects that are tagged with a transponder or micro-transponderdevice.

BACKGROUND OF THE INVENTION

Modern cellular telephones are becoming more flexible and, essentially“software defined”. Thus, they often operate at different frequencies,modulation types and data rates in a completely transparent fashion tothe user. Often, these phones have short message services and/orinternet browsing capabilities. In general, communication data rates andsignal bandwidths have increased with the desire to operate them asPDA's (personal digital assistants). In addition, it is quite common foreven generic cellular telephones to have an embedded GPS receptioncapability, which often isn't directly available to the user, but isemployed for emergency position finding or other purposes. Often thesignal processing in cellular telephones is implemented in programmableDSP's or digital signal processing chips. This lends great flexibilityto said cellular telephones.

These cellular telephones have rechargeable batteries, which are oftenrecharged at night, which minimizes the volume and mass of the battery.

Separately, there has of late been a very large increase in the use ofGPS devices for a variety of purposes, very often automobile navigation,where they are extremely effective. There has also been interest inlocation of persons, animals, and things. In many cases, the GPSsolution to this is impractical, because of energy consumption, physicalsize, and/or inadequate access to the sky overhead.

Some methods for locating an object are known in the art. A missingvehicle locator system is described in U.S. Pat. No. 5,418,736 issued toBird. The vehicle locator system uses one or more GPS systems inconjunction with a GPS antenna, a receiver/transmitter, a telephone withassociated antennas, and a modern mounted in a vehicle whose position isto be monitored. A paging request is issued and received by a pagingresponder in the vehicle. The paging request causes the modem tointerrogate the GPS receiver to determine the current position of thevehicle. The current position of the vehicle is transmitted via acellular telephone link to notify a vehicle location service center ofthe current location of the vehicle. Other known location determinationtechniques include the use of a Loran or a Glonass satellite basedsystem.

Another object location system is described in U.S. Pat. No. 5,576,716to Sadler for locating lost or stolen property. This location systemincludes a GPS module, a microcomputer, a modem, and a telephone, all ofwhich must be installed in the vehicle. The system described regularlyand automatically computes the position of the property for transmissionvia the phone link to a central receiver/transmission station.

Low power transmissions are subject to signal corruption due to noise,static, and signal interference. Extracting information from a signal inthe presence of such interference and noise is very difficult when theinformation signal is of the same order of magnitude as the noisesources. The presently described invention identifies various noiseproblems from the conventional solutions and provides a new and novelsystem, method, and apparatus that is arranged to extract signals from atransmission using very low power in a small scale object locationsystem.

SUMMARY OF THE INVENTION

This invention resides to location and communication systems that can beutilized for locating people, pets and other objects with a softwaredefined radio set. A personal electronic device (PED) such as a cellulartelephone, personal data assistant (PDA) or other device includes asoftware defined radio set can be configured for operation as a locatordevice. The PED transmits a signal. A transponder or micro-transponder(MT), tagged to an object, replies to a transmission received from thePED. The PED based locator is arranged to calculate a distance betweenthe PED and the MT using the time-of-flight (TOF) between thetransmission and the receipt of a reply. The absolute geographicposition of the PED can be determined using satellite navigationinformation, while the position of the MT relative to the PED can bedetermined from the TOF information.

A method is disclosed for determining the position of a transponder witha radio transceiver in personal electronic devices that also eachinclude a satellite navigation system. A preferred method comprisesidentifying a target ID associated with the transponder; sending atransponder location request to each of the personal electronic devices;and receiving a location and distance measurement from each of thepersonal electronic devices after sending the transponder locationrequest. A location associated with the transponder is calculated fromat least a portion of the received location and distance measurementsby: determining a circle for each received distance measurement at ageographic position associated with the corresponding received location;identifying a common point area that is created by an overlap ofcircles; and identifying the location and distance to the transponderbased on the identified common point area.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments are described with referenceto the following drawings:

FIG. 1 is a block diagram illustrating a personal electronic device thatis arranged for operation as a locator of cooperative transponder tags;

FIGS. 2A-2C are diagrams illustrating example operating environments fora personal electronic device arranged for operation as a locator ofcooperative transponder tags;

FIG. 3 is a block diagram illustrating example audio processingfunctions for a personal electronic device arranged for operation as alocator of cooperative transponder tags;

FIGS. 4A-4E are diagrams illustrating the use of the satellite basednavigation in conjunction with one or more personal electronic deviceseach arranged for operation as a locator of cooperative transpondertags;

FIGS. 5A-5B are flow charts illustrating example process flows for alocator software application that can be used in one or more personalelectronic devices each arranged for operation as a locator ofcooperative transponder tags;

FIGS. 6A and 6B are detailed block diagrams illustrating an examplepersonal electronic device arranged for operation as a locator with anexample cooperative transponder tag;

FIG. 7 illustrates an example transmitter;

FIG. 8 is a diagram illustrating a set of frames formatted fortransmission;

FIGS. 9A and 9B are diagrams illustrating the timing acquisition for anexample communication system;

FIGS. 10A-10B are example diagrams for example receivers;

FIG. 11 is a flow-chart for an example transmitter;

FIGS. 12A-12B, 13A-13B, and 14 are flow-charts for example receivers;

FIG. 15A is an example graph for effective change in distance during arotation through 360 degrees;

FIG. 15B is an example graphs for correlation phase information from arotation through 360 degrees;

FIGS. 16A-16C are example illustrations for a look-around procedure thatis employed by a user in a search and locate mode;

FIG. 17 is an example diagram illustrating single ping mode, slow pingmode, and fast ping mode;

FIGS. 18A-18D are example flow charts for example mode selectionfeatures for an example locator; and

FIGS. 19A-19B are example flow charts for example mode selection in anexample micro-transponder (MT), all arranged in accordance with thepresent disclosure.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure now will be described more fully hereinafter withreference to the accompanying drawings, which form a part hereof, andwhich show, by way of illustration, specific exemplary embodiments forpracticing the invention. This disclosure may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope to those skilled in the art. Among other things, thepresent disclosure may be embodied as methods or devices. Accordingly,the present disclosure may take the form of an entirely hardwareembodiment, an entirely software embodiment or an embodiment combiningsoftware and hardware aspects. The following detailed description is,therefore, not to be taken in a limiting sense.

Throughout the specification, and in the claims, the term “connected”means a direct electrical connection between the things that areconnected, without any intermediary devices. The term “coupled” meanseither a direct electrical connection between the things that areconnected or an indirect connection through one or more passive oractive intermediary devices. The term “circuit” means one or morepassive and/or active components that are arranged to cooperate with oneanother to provide a desired function. The term “signal” means at leastone current signal, voltage signal, electromagnetic wave signal, or datasignal. The meaning of “a”, “an”, and “the” include plural references.The meaning of “in” includes “in” and “on”.

Briefly stated, the present disclosure relates to location andcommunication systems that can be utilized for locating people, pets andother objects with a software defined radio set. A personal device (PED)such as a cellular telephone, personal data assistant (PDA) or otherdevice that include a software defined radio set can be configured foroperation as a locator device. The PED transmits a signal to atransponder or micro-transponder (MT) that is tagged to an object isarranged to reply to a transmission received from the PED. The PED basedlocator is arranged to calculate a distance between the PED and the MTusing the time-of-flight (TOF) between the transmission and the receiptof a reply. The absolute geographic position of the PED can bedetermined using satellite navigation information, while the position ofthe MT relative to the PED can be determined from the TOF information.

As will be described, the PED and the MT each include a receiver and atransmitter. The communication signals from the transmitters are encodedwith a unique ID code. The communication signal consists of a sequenceof encoded transmissions, where each sequence is arranged to provide aportion of clock synchronization and calibration information. Eachreceiver validates the ID code for the transmission, and decodesinformation. The frequency, phase, and starting time of the codedtransmission sequence is determined by the transmission sequence itselfsuch that clock recovery can be performed without additionalinformation. The MT can be a wearable circuit such as a band or collar,affixed to an object, embedded in an object, or an implantable bionicdevice.

Block Diagram for a Locator Based Personal Electronic Device (PED)

FIG. 1 is a block diagram illustrating a personal electronic device(100) that is arranged for operation as a locator of cooperativetransponder tags, arranged in accordance with the present disclosure.The personal electronic device or PED can be any device that includes asoftware defined two-way wireless radio set including but not limitedto: cellular telephone devices, personal data assistance (PDA) devices,combined cellular telephone/PDA devices, as well as others.

The example personal electronic device (PED) of FIG. 1 includes aprocessor (110), a software system (120), a satellite navigation system(130), and a configurable two-way wireless radio set (140). Theprocessor (110) is arranged to interact with the software system (120)to perform a variety of functions. The software system (120) includes aradio control logic portion (121) that is used for configuring thetwo-way wireless radio set (140), and also a locator logic (122) that isused to determine and/or track the location of one or more transpondertags (not shown). The two-way wireless radio set (140) can include avariety of functional blocks such as radio configuration logic (141),baseband processing (142, e.g. DSP based baseband processor), and atransceiver radio set (143). The described blocks may be combined orseparated into other functional blocks based on the use of a particularchipset or the overall system implementation as may be desired.

The satellite navigation system (130) can be of any variety such as GPS,Loran, Glonass, and Galileo based satellite navigation systems. Thesystem can be provided as a single chip solution, a chip set, orintegrated together with one or more other functional blocks as may bedesired.

The processor (110) can be any variety of processor including processorcores or integrated circuits. Example processors include any one of amicro-processor, a micro-controller, a complex instruction set computer(CISC) processor, a reduced instruction set computer (RISC) processor,an application specific integrated circuit (ASIC), or a programmablelogic device (PLD).

The necessary software and/or firmware for the processor can be providedin a memory circuit (not shown) or some other storage medium (e.g., harddisk drive, optical disk, etc.). Example memory circuits include randomaccess memory (RAM) circuits, dynamic random access memory (DRAM)circuits of all varieties and static random access memory (SRAM)circuits, to name a few. Some example memory circuits are read-onlymemory (ROM) circuits, while others can be programmable read-only memorycircuits (PROM) such as EPROMs, EEPROMS, and other non-volatile memories(NVM) such as flash-type memories and other varieties.

In operation, the two-way wireless radio set (140) is configured inresponse to software applications that are executed by the processor(110). During the configuration process, the radio configuration logic(122) in the software system (120) is used to generate configurationdata (CONFIG) that is used by the two-way wireless radio set (140), suchas by the configuration logic (141). The configuration logic (141) isused to cooperate with the baseband signal processing (142, e.g., DSP)and the radio set transceiver (143) to adjust transmit and receivefrequencies, data encryption and decryption, and other functionsnecessary for use of the two-way radio for locating a transponder. Thetwo-way radio set (140) may also cooperate with the processor (110)and/or satellite navigation systems (130) directly as may be necessary.Antennas (150) are used with the two-way radio set (140) to transmit andreceive.

The personal electronic device (PED) can optionally be configured tomake use of the satellite navigation capability (e.g., GPS set) todetermine an absolute position of the PED, and to very preciselyfrequency correct its quartz crystal oscillator.

The personal electronic device (PED) may include any variety of userinterface means such as user inputs (101) from a keyboard, keypad,joystick, button, a microphone, or another reasonable user input means.Also, the user interface means may include any variety of outputmechanisms such as an audio device (102), a display device (103), or anyother reasonable output means.

Example Operation Environment

FIGS. 2A-2C are diagrams illustrating example operating environments fora personal electronic device arranged for operation as a locator ofcooperative transponder tags.

As illustrated by the operating environment (200) of FIG. 2A, an examplepersonal electronic device (PED 210) may includes a display (211), auser interface (UI 212), a microphone (213) and a speaker (214). Anexample display (211) is an LCD display, either color or monochromatic,such as may be found in a cellular telephone. The user interface (212)can be a touchpad, touchscreen, a keypad as well as any other known userinterface that may be desired. Example speakers (214) include allvarieties of conventional speakers including electrostatic speakers andpiezo devices. The microphone (213) can be used as a voice inputmechanism as will be described later.

During operation the PED (210) is carried by a user. The user activatesthe location mode and designates the identity of the target (e.g.,TARGET ID), such as via the microphone (213) input of the userinterface. After activation of the location mode, the two-way radio(e.g., see FIG. 1) is configured for communicating with the taggedperson or object (220) and begins such communication between the PED(210) and the transponder (220) in the tag. The roundtrip time-of-flight(TOF) of the communication can be used to determine a distance betweenthe tag's transponder (220) and the PED (210). The satellite navigationsystem (215) will monitor the location and velocity of the PED, whilethe software system (216) via the various processing functions willdetermine the apparent velocity and distance to the tagged object orperson. Both of the velocities can be used together to determine aprecise location, direction and distance between the PED (210) and thetransponder (220). Moreover, the satellite navigation system (215) canidentify an exact geographic location (e.g., lat1, long1) of the PED(210) so that the PED (210) can compute an exact geographic (e.g., lat2,long2) location of the tag's MT.

As illustrated by the operating environment (230) of FIG. 2B, multiplepersonal electronic devices (PED 210) can be used collaboratively todetermine an exact location of a micro-transponder device (MT 220). ThePEDs may each be arranged as described with reference to FIG. 2A, whereeach PED includes facility to measure a distance to MT 220. For examplefive PED devices are each located at a different geographic position(e.g., Location PED1-Location PED5) relative to the location (LocationMT) of the MT (220). Each PED device can then be requested to make adistance measurement (e.g., Distance 1-Distance 5), and report thedistance measurements to some form of central processing on either oneof the PEDs (e.g., the requesting PED) or on a server within thecommunication network. The locations of the PEDs and the distancemeasurements together can form a set of geographically arrangedoverlapping circles that include a common point that corresponds to thelocation of the MT (220). The overall method of determining the positionwill be described in further detail with respect to FIGS. 4A-4E.

As illustrated by the operating environment (240) of FIG. 2C, a seriesof cellular towers (BTS) are arranged in a cellular telephone network(120) that facilitates communications to PEDs that includes cellulartelephony capabilities. Cellular communications from the cellular towersare managed by a back-end server that can be operated by the cellulartelephone company. A location process can be operated on a server sothat a messaging processing system (e.g., SMS messages) can be managedto facilitate location processes.

In some example, a PED can initiate a search process by transmitting amessage requesting a search for an MT by the location processes operatedwithin the cellular telephone company's server. The location processthen accesses a database through a database server to query forlocations associated with the identified MT. Candidate PEDs areidentified based on their relative position to the MT, and then amessage can be communicated to those PEDs requesting a distancemeasurement. PEDs can then configure their radio sets to search for theMT, measure any distances to the MT, and report those measurements backto the server for analysis. The PEDs can also report their location tothe server using their own satellite navigation system as previouslydiscussed. The server then maintains a log of cell phone IDs for eachPED, including their reported distance measurement and their currentposition. Once enough measurements are assembled, the server candetermine the precise geographic location of the MT and communicate theresult back to the requesting PED.

In some other examples, a none PED device can submit a search requestsuch as from a personal computer via an internet based communication.The communication can be established directly with the cellular companyvia a website, or via some other mechanism such as an SMS message thatis initiated over the internet. The server can again execute a locationprocess to search for the identified MT, and report the search resultsback to the personal computer. Many other examples are alsocontemplated, and the above-described networked systems are merelyprovided as illustrative examples.

Example Audio Processing

FIG. 3 is a block diagram illustrating example audio processingfunctions (300) for a personal electronic device (PED), arranged inaccordance with features of the present disclosure. In particular, FIG.3 illustrates example audio processing function that can be utilized foroperating the PED by speech interpretation.

Onboard audio processing (310) for the microphone (311) may include ananalog-to-digital converter (ADC 312) and digital signal processing (DSP313). The audio processing (310) can be found in most conventionalcellular telephones. In this instance however, the speech processingfunctions (333) are added to the software system (330) so that theprocessor (320) recognizes voice/speech based input (301) for an actioncommand and a target ID that is used by the processor (320) to activatethe locator mode.

For example, a location transmission is initiated by the user of thecellular telephone by a voice command such as “Find Fluffy.” The word“Find” is interpreted as an action command to enter the locator mode,while the word “Fluffy” is interpreted as a target ID for the locatorlogic (331) in the software system (330). The radio configuration logic(332) in the software system (330) is utilized to configure the two-wayradio set in the PED for a location operation. The locator logic (331)in the software system (330) is used by the processor (320) so that thetarget ID for “Fluffy” is coded into the transmission sequence for aspecific transponder that is associated with “Fluffy”, most likely a cator dog in this example.

After the locator mode is active, a coded sequence that is specificallycoded for the “Fluffy” transponder is transmitted. The transponder,which can be in a sleep mode that “wakes up” every few seconds or so(for e.g., 150 microseconds), and collects samples of the appropriateradio spectrum while active. If an appropriate set of sequences isfound, the transponder will reply with a precisely timed reply, which isapproximately delayed in time by the time-of-flight, or round trip timeof the communication.

The PED is also configured under software control (e.g., software system330) to capture samples of the radio spectrum at a predicted time forwhen the reply sequence from the transponder is expected. The replysequence is delayed by the round-trip time of flight of the radiosignals plus a fixed time offset. From this signal capture, the distanceto the transponder can be determined as well as other auxiliary data.

Example Satellite Navigation Operation

FIGS. 4A-4C are diagrams illustrating the use of satellite basednavigation (e.g., GPS) in conjunction with a personal electronic device(PED) arranged for operation as a locator of cooperative transpondertags.

FIG. 4A illustrates a locator system (400) where a personal electronicdevice (410) is configured to operate as a locator that communicateswith a transponder or micro-transponder (420) such as may be found on atag. The PED (410) is moved by the user in any arbitrary direction whenthe locator mode is active. During a first instance of time (e.g.,time=t0) the direction of travel is designated as direction A, while ina second instance of time (time=t1) the direction of travel isdesignated as B. The velocity of the PED (310) corresponds to a firstvelocity (V1) when the direction of travel corresponds to direction A,and a second velocity (V2) when the direction of travel corresponds todirection B. These velocities for the PED (310) are retrieved from thesatellite navigation system (e.g., GPS), as are the known geographicpositions (e.g., lat/long) of the PED (310).

FIG. 4B is a graphical diagram (430) illustrating a first velocityvector (VA). Velocity vector VA is positioned from an origin at thecenter of a circle, and extending in-between two points A and A′. PointsA and A′ correspond to the apparent velocity associated with thedirectional vector that is determined by processor via the locatorlogic, which occurs at the same time that velocity V1 is retrieved fromthe satellite navigation system.

FIG. 4C is a graphical diagram (440) illustrating a second velocityvector (VB). Velocity vector VB is similarly positioned from an originat the center of a circle, and extending in-between two points B and B′,wherein points B and B′ correspond to the apparent velocity occurring atthe same time that velocity V2 is retrieved from the satellitenavigation system.

The direction of the transponder (420) relative to the PED (410)corresponds to the common direction between these two velocity vectors(VA, VB). Since A′ and B are mapped at the same location, the ambiguityin direction is resolved and the other directions are discarded. Thisprocess is accomplished by analyzing the true velocity of thelocator/PED with respect to the earth's reference system, andcorrelating this velocity with the apparent frequency and cadence shiftof the signal from the “Fluffy” transponder.

FIG. 4D is a graphical diagram (450) illustrating a locationdetermination from a PED that performs a series of distance measurementsas the PED moves through a path of travel. At time=t1, the PED islocated at a first location (LOCATION 1) and calculates a first distancemeasurement (DISTANCE 1) based on a time-of-flight (TOF). At time=t2,the PED is located at a second location (LOCATION 2) and calculates asecond distance measurement (DISTANCE 2) based on a time-of-flight(TOF). The circles illustrated in FIG. 4D illustrate a constant distanceabout the location of the PED at that point in time. The two circlesintersect at two points, where one point corresponds to the location ofthe transponder. It is important to note that an ambiguity exists atanother intersection point, which can easily be resolved by additionalmeasurements as the path of travel continues.

FIG. 4E is a graphical diagram (450) illustrating a locationdetermination from either one PED that performs a series of distancemeasurements as the PED moves through three points along a path oftravel, or via multiple PED devices that report their location anddistance measurement such as described previously for FIGS. 2A-2C. Afirst PED (PED1) is located a first location (Location PED1), andmeasures a first distance (DISTANCE 1) to the transponder. A second PED(PED2) is located a second location (Location PED2), and measures asecond distance (DISTANCE 2) to the transponder. A third PED (PED3) islocated a third location (Location PED3), and measures a third distance(DISTANCE 3) to the transponder.

Three circles are illustrated to demonstrate a constant radius ofdistance about the location at the time of measurement by a PED.Although each circle may overlap at two places, leaving an ambiguity inthe exact location of the transponder, the use of all three measurementstogether results in a single location of the transponder (MT location).As such the above description illustrates that a network of PEDscommunicating either through a server or directly to one another caneasily be used as an opportunistic model to collaboratively identify thetransponder's precise location.

Example Process Flow for PED Locator Operation

FIGS. 5A-5B are flow charts illustrating example process flows (500) fora locator software application that can be used in one or more personalelectronic devices (PEDs) arranged in accordance with the presentdisclosure.

As illustrated by FIG. 5A, a first process (510) can be used by each PEDto collect information based on its own collection of distancemeasurement information. First user inputs are processed (511) such asfrom a user interface, a micro-phone, etc. The command and target ID arethen extracted (512) from the user input such as via a speechrecognition system. Then, the 2-way radio system is configured to alocator operation (513). Velocities are then retrieved from thesatellite navigation system (514), as well as the current locationassociated with the PED (515). Apparent velocities are then identifiedwith the locator system (515), and the direction and distance from thelocator to the transponder are determined using the describedcorrelation operations (516). The display of the PED is then updated(517) to indicate a direction, distance, and/or exact locationassociated with the target ID. This process (514-518) repeats fromdecision block 519 until the locator mode is disabled, such as viaanother user initiated input (518).

As illustrated by FIG. 5B, a second process (520) can be used by a PEDto collect information based on a collection of distance measurementsfrom multiple PEDs using a search process. First user inputs areprocessed (521) such as from a user interface, a micro-phone, etc. Thecommand and target ID are again extracted (522) from the user input suchas via a speech recognition system. Then, a message is transmitted(e.g., an SMS message, email request, etc.) from the requesting PED tothe locator process (523) such as might be managed by a server from acellular telephone company. The location process includes processingsteps 524-529.

At step 524, candidate PEDs are identified for requesting a transpondersearch via distance measurements. Each candidate PED is then sent alocation request (525) to search for the identified transponder (e.g.,via a TARGET ID). Each PED that receives the location request willsearch for the targeted transponder, identify its own location such asvia a satellite navigation system, calculate a distance measurementusing the described time-of-flight measurements, and report the locationand distance measurement back to either the requesting server or therequesting PED. At block 526, the distance and location measurements arereceived by the location processes. At block 527, the targettransponder's location is determined such as previously described withreference to FIG. 4E. This process (524-527) repeats from decision block528 until the distance measurement and exact location of the transponderis determined. Proceeding to block 529, the calculated location of thetargeted transponder is sent as a message back to the requesting PED.

Example Detailed System for PED/MT

FIGS. 6A and 16 illustrate an example communication system (600) thatincludes a PED based locator (610) and a MT (620) arranged in accordingwith at least one aspect of the present disclosure. The PED (610) isarranged to transmit a sequence over a communication channel, while theMT (620) is arranged to transmit back to the PED (610) over thecommunication channel in a half-duplex fashion.

The example PED (610) includes a processor, an antenna (ANT1), asoftware configured two-way radio set, memory, a satellite navigationsystem, and a series of user interfaces. The memory includes, amongother things, a mode control logic, locator logic, and a radioconfiguration logic. The processor is arranged to configure the softwareconfigured two-way radio set under control of various softwareapplications such as those illustrated in the memory.

When the personal electronic device is changed into a locator mode, theprocessor is arranged to cooperate with the radio configuration logic toconfigure the two-way radio set. For example, a number of functionalblocks for the two-way radio set can be configured to include: abase-band signal processing block, a sequence generator block, alow-pass filter block, a transmitter block, a receiver block, atransmit/receive switch block, and a band-pass filter block. Thetransmitter and receiver block is illustrated as coupling to the antenna(ANT1) through a transmit/receive switch (SW1) based on the operatingmode being either transmit (e.g., TX1 asserted) or receive (e.g. RX1Nasserted). A transmission sequence (e.g., TSEQ) is coupled to the firsttransmitter block when transmission commences, where the sequence isdetermined by an ID code associated with the target tag (e.g., IDCODE=f(TARGET ID)). The receiver block is coupled to the baseband andsignal processing block. Timing parameters for the transmitter,receiver, baseband processing, and the processor are provided by a timecontrol block, which is illustrated as various clock signals (CLK1,BBCLK1, TCLK1, and RCLK1).

The processor receives inputs from any variety of user input devicessuch as an audio input stream from a microphone such as previouslydescribed, a keypad type device, a touchscreen or touchpad type device,or any other reasonable input device. The processor is also arranged toprovide output to any variety of output mechanisms such as an audiooutput (e.g., speaker) or a display output (e.g., LCD display).

The processor is arranged to coordinate the operations of managingoperating modes for the PED (610), managing memory access, execution ofsoftware application programs, performing computations, managing userinterfaces, and interfacing with the satellite navigation system forlocation based calculations. The processor also coordinating theoperations for the software configured radio set such as basebandprocessing, signal analysis, memory buffering, input processing. Thememory processing can include random access memory (RAM), read-onlymemory (ROM), as well as non-volatile memory (NVM) such as Flash memory,battery backed up RAM, EEPROM, as well as other NVM type technologies.

Additional antennas (e.g., ANT1B) can also be coupled to the receiverblock of the PED device such as through an additional switch (notshown). For this example, the PED can multiplex between the variousantennas. The various antennas can be arranged (e.g., orthogonal to oneanother) as diversity antennas that are used to gain additionalinformation about signal strength, distance and Doppler, etc.

The example MT (620) device includes a second antenna (ANT2) that iscoupled to a second transmit/receive switch (SW2). The secondtransmit/receive switch (SW2) is coupled to a second transmitter blockand a fourth receiver block in response to another control signal(TX2/RX2N). A reply sequence (e.g., RSEQ) is coupled to the secondtransmitter block when transmission commences, where the sequence isdetermined by the ID code. The second receiver block is arranged toprovide in-phase and quadrature signals (I and Q) that are captured in abuffer (e.g., a memory buffer such as a digital buffer or an analogsample buffer). The capture buffer is coupled to a correlator in abaseband signal processor block, which can provide both direct formcorrelation and FFT correlation functions. The FFT correlator isarranged to provide a circular correlation function of the received I/Qdata with the complex I/Q data related to the ID code. A signal analyzerand a processor are both arranged to receive the data output from thecorrelator for evaluation. Time control is provided to the transmitter,receiver, and the processor in the form of various additional controlsignals (TCLK2, RCLK2 and CLK2). The processor receives inputs andcoordinates the operation of the correlator, signal analysis, sequencegeneration, memory buffering, and other related tasks. The memory forthe processor can include random access memory (RAM), read-only memory(ROM), as well as non-volatile memory (NVM) such as Flash memory,battery backed up RAM, EEPROM, as well as other NVM type technologies.

Current technology systems for locating people and things have a rathershort battery life, which can limit their use. The present disclosuredescribes a small device (e.g., a transponder or a micro-transponder)that has a long battery life by suspending energy consumption untiloperation is required. Since the MT device needs to be in an activestate for very brief intervals, the battery life is extendedsubstantially. Although cellular telephone technologies can be used todetermine position in conjunction with a global positioning system (GPS)set, such as a system is inappropriate for the MT since the energyrequired to operate conventional cellular telephones even in a standbymode will rapidly deplete small batteries. In addition, a GPS set in anMT device would awaken from sleep, and perform a cold start locationfix, which process will consume a considerable amount of energy thatagain rapidly depletes the battery. The present disclosure contemplatesthat a portable location technology for the MT is preferably operatedintermittently to minimize power consumption, and thus addresses some ofthe problems from conventional location determination techniques.

The present disclosure has analyzed and identified problems with currentDoppler shift technology such as found in GPS signals, which render thenunusable for the MT in the present system. Although GPS signals may bedetected efficiently by means of FFT correlation, there areapproximately 28 GPS satellites that include a significant level ofDoppler ambiguity from about +15 ppm. For a GPS signal of 1.5 GHz and acapture interval of 1 msec, a Doppler shift of roughly 22 KHz maximumrequires on the order of several tens of Doppler bins or correlationattempts to identify the Doppler shift. The processing efforts necessaryto utilize a conventional GPS technology are unacceptable for thepresently disclosed use. For example, the MT in the current disclosureis searching for a single code, and in addition, need not contend withhuge velocities, and thus does not require any Doppler bins. Moreover,the present disclosure describes an apparatus and system that hasreduced capture times relative to conventional technologies, where themagnitude of the processing is reduced by approximately two orders ofmagnitude.

Communication and Locating Issues

Frequency and phase information in the MT is initially recovered fromone portion of the transmission from the PED, and further refined usinga bootstrapping process. Timing location within the frame (e.g., coarsetiming) is recovered in another portion of the transmission from thePED. After the timing, phase and frequency are recovered, data receptioncan be scheduled with a degree of certainty. The data is extracted and areply message is transmitted from the MT back to the PED, where similarsignal processing functions are performed by the reconfigured radio setin the PED. The carefully corrected round-trip time of the transmissionsequence is used to identify distance between the PED and the MT. Asynthetic round-trip Doppler shift, which is independent of the MT'sinternal clock, can be measured to and correlated against the relativemotion of the PED and MT to assess the magnitude of a directional vectorbetween the PED and the MT.

The presently described system has the ability to identify location of aMT with a PED configured locator utilizing an asymmetric transmissionsystem. The signals captured by the MT will typically not be aligned intime with the start and end of a complete pattern in the sequence (e.g.,a 2047 chip sequence). However, the PED configured locator is arrangedto transmit repeated patterns over time in the sequence. The MT isarranged to cyclically capture a complete pattern in the sequence, eventhough the captured pattern may be rotated in time relative to the startand end of a complete pattern. A circular correlator can be used toevaluate the captured signals such that the captured signals areproperly identified by the MT, despite the rotation status of thepattern. Since the MT does not have a priori knowledge of the timingrelated to transmission and reception from the PED, circularcorrelations of the received transmissions are used by the MT todetermine the fine and coarse timing. A circular correlation is acorrelator that operates on a sequence of fixed length, where thesequence may be circularly shifted in time such that the beginning ofthe original sequence may be received in the shifted sequence after theend of the original sequence. While a general correlator may not givevalid timing information, the circular correlation will provide validtiming information when the captured signals are not aligned in timewith the start and end of a complete pattern.

The presently described asymmetric transmission system can be configuredsuch that the MT receives a relatively high power transmission of astructured signal from the PED, while the reply or acknowledgementtransmission from the MT to the PED is a very low power transmission. Anexample MT is configured to operate in a very low power “inactive” modeor “sleep mode”, where the MT “activates” or “wake-ups” for briefintervals to listen for the transmission from the PED. The MT correlateseach piece of its received structured signals to determine if thesesignals are coded with an identification code (ID Code) that isspecifically associated with the MT. The MT also determines the precisefrequency, timing, phase, and cadence for which a reply transmission canbe transmitted back to the PED from the received structured signals. Thereply transmission that is transmitted from the MT to the PED is a verylow power transmission of short duration (a short structured signal)such that significant battery life is conserved. Although the replytransmission is a very low power transmission, the signal processingfunctions in the PED can be configured to utilize an integration andcircular correlation technique to increase the signal-to-noise level ofthe captured reply transmission.

In the presently described system, a reply transmission signal istransmitted back to the PED from an MT, where the MT synthesizes timing,frequency, phase, and cadence for the reply transmission from signalsthat are received by the MT from the PED. The frequency of the replytransmission from the MT differs from the original frequency from thePED's transmission by a Doppler shift (ignoring other noise and minorerror sources). As such, the PED can predict the reply transmissionfrequency with a very small margin of error. The potential uncertaintyof the reply transmission frequency is small enough so that the phaserotation over several tens of transmission sequences is much less thanone turn (one phase rotation through 360 degrees). This allows the PEDto sample the reply transmission and add (or integrate), either in theanalog domain or the digital domain, the respective samples from replytransmission sequence. Since noise sums as a square root and signal sumslinearly, the signal-to-noise ratio for the captured signal isincreased, allowing reception of a much lower level signal than wouldotherwise be the case without the use of exhaustive computation.

Example PED Based Locator

FIG. 6A illustrates an example PED based locator that is arranged tocommunicate with an example MT. The MT is arranged (e.g., by a sleeptimer) to wake up at pre-determined intervals and receive a codedtransmission signal (e.g., COM13). The coded signals are received andevaluated using a variety of signal processing methods such as digitalsignal processing, analog signal processing, Fast Fourier Transform(FFT), correlation, inverse FFT (IFFT) to name a few. The MT evaluatesthe received coded signals to determine if the signals are specificallyidentified with the MT (e.g., by a unique ID code). Through the varioussignal-processing functions, various internal signals and parameters arevaried such that time, frequency and phase alignments for receiving andtransmitting coded information are successively refined (e.g., throughdigital control mechanisms) for accurate processing. The MT, using asits time base the Doppler shifted frequency of the signal from the PEDlocator, subsequently transmits a reply sequence back to the PEDlocator, which is similarly coded. The PED based locator receives thecoded transmission, and processes the incoming signals in a similarfashion as the MT.

The PED based locator includes a processor that can be any appropriateprocessing means including but not limited to at least one:micro-processor, micro-controller, CISC processor, RISC processor,application specific integrated circuit (ASIC), to name a few. Theprocessor is arranged to: receive and evaluate inputs, control outputs,log data, retrieve logged data, and execute programs. The processor isthus arranged to communicate with any number of circuit components suchas: a time control circuit, an input circuit, a display output circuit,an audio output or input circuit, a storage circuit, and a memorycircuit.

Example inputs can be from any number of input devices (or user inputmeans) such as: an interrupt signal, a wake-up timer, a keyboard device,a keypad device, one or more buttons or keys, a touch-screen (passive oractive), a touch-panel, a joystick device, a joy-pad device, a mousedevice, a pointing device, a touch-pad device, a pressure sensitiveinput device, or another processor and an input generated by a softwareprogram. In some examples, sound can be used as an input to the PED viaaudio input processor such as an analog-to-digital converter (ADC)circuit or a coder-decoder (CODEC) circuit that includesanalog-to-digital conversion means. A microphone can be built into thePED or externally coupled to the PED through a microphone port for soundinput purposes, where signals received by the microphone into a digitalsignal that can be interpreted as an input. The sound-based input can bestored for further use (e.g., a sound file for playback or recognitionpurposes) or interpreted as a voice input that can be utilized by thePED. In some implementations, a voice-to-text interpreter can beincorporated into a hardware solution that is arranged in communicationwith the processor. In some other examples, voice recognition undersoftware control implemented by the audio input processor to operate asa voice input means that generates an example input.

Audio output circuits can be used as an indication means for reportingaudible information to a user of the PED device, as well as to providenavigation and location information. The audio output circuit caninclude an audio output device and an audio output processor. The audiooutput processor is arranged to cooperate with the audio output deviceto provide an audible notification to the user. The functions of theaudio output device and the audio output processor can be combined insome implementations. The audio output device can be an audio drivercircuit for a headphone type device or a speaker type device. In someexamples, a speaker or a piezo device is included in the PED to providesound output. In another example, an audio output port such as aheadphone jack can be provided in the PED for a user to connect aheadphone type device, or perhaps an external speaker connection.

The audio output processor can be a single tone generator circuit, apolyphonic tone generator circuit, a polyphonic synthesizer circuit, avoice synthesizer circuit, a MIDI playback circuit, or a sound playbackcircuit. In some examples, the audio output processor includesdigital-to-analog conversion means such as from a digital-to-analogconverter (DAC) circuit or from a CODEC circuit. The voice synthesizercircuit can include a text to speech interpreter. The voice synthesizercan also be arranged to provide various regional voice affectations andlanguage accents, such as male and female voices, robotic voices,English accents, French accents, Spanish accents, etc. In some examples,the audio output processor is arrange to provide music playback that canbe in any desired format such as a lossy compressed sound file, anon-lossy compressed sound file, or an uncompressed sound file. In otherexamples, the audio output processor device is arranged to provideplayback of previously recorded sounds or user recorded sounds. Therecorded sounds can be voice messages such as can be provided incharacter voices (e.g., cartoon characters), recordings of celebrities,or as impressions of recognizable voices. In some examples, the audiooutput processor can be combined in function with the audio inputprocessor previously described.

Display circuits can also be used as an indication means for reportingvisual information to a user of the PED device, as well as to providenavigation and location information. Example display circuits canprovide any appropriate video output such as, for example: an LED typedisplay, an LCD type display, an active display, a passive display, ablack and white display, a monochromatic display, and/or a colordisplay. Other examples display circuits can be discrete arrangement ofLEDS, seven segment displays, as well as other light emitting devicesthat can be used for reporting visual information. In some examples, theuser interface can be integrated with the video output device such as,for example, a touch screen that is integrated with an LCD display. Inother examples, the user input interface is separate from the videooutput device.

The processor in the PED of the present disclosure can be arranged tocooperate with a compass sensor device (not shown) or some similar meansfor determining a rotational position of the PED. The compass sensor canbe an integrated circuit, a discrete circuit, or some other device thatis arranged to provide compass sensor information that is related to adirectional orientation of the PED. The compass sensor can be a digitalcompass device or an analog compass device that is arranged to work withan analog-to-digital converter, for example, to provide a comparablefunction.

In some examples, distance can be reported with display circuit in analphanumeric representation (e.g., 100, 100′, 100 ft, 100 m, etc.). Inother examples, distance can be reported in a graphical representationsuch as an icon, a line, or other graphical shapes. Similarly, directioncan be reported in either an alphanumeric representation (e.g., N, S, E,W, NE, SE, NW, or SW) or in a graphical representation. Any combinationof graphical and alphanumeric representations can also be made.

The processor is arranged to apply mode control logic in response to avariety of user inputs for activating and deactivating a variety ofoperating modes as will be described. The mode control logic and anyrelated settings for the PED can be provided in software form or as afirmware such as a read-only memory (ROM) that is loaded into aconventional memory for execution by the processor, or by someequivalent mechanism such as a non-volatile memory (NVM), a flash memorydevice, and hard-coded instructions in a micro-controller, to name afew. In another example, the processor and memory can be replaced with aprogrammable logic device (PLD), a specially designed circuit such as anapplication specific integrated circuit (ASIC), as well as othersdevices that are arranged to provide similar functionality.

When the two-way radio set in the PED is configured for a locator mode,the PED is operated to send a transmission that consists of a series ofcoded signals. The code is generated by a unique identifier (e.g., an IDCode) that is associated with a specific MT. A sequence generator isarranged to evaluate the unique identifier and create a transmitsequence. After the coded sequence is generated for the uniqueidentifier, additional information is encoded into the transmitsequence. In one example, the additional information can becommand/control instructions for the MT. Only one sequence need betransmitted to accomplish communication, timing synchronization, andsequence validation. The output of the sequence generator (e.g., TSEQ)can be filtered such as by a low pass filter (LPF1) prior to couplingthe signal to the transmitter block.

The transmitter block is arranged to carrier modulate (e.g., multi-phaseshift keying, binary phase shift keying, quadrature phase shift keying,differential phase shift keying, continuous phase modulation, multipleamplitude and phase shift keying, etc.) the coded signals with a carrierfrequency, a spread spectrum carrier, and/or a frequency hopping method.The transmit-receive switch (SW1) is arranged to couple the carriermodulated coded signals to the antenna (ANT1) during the transmitsequence. A band-limiting filter (e.g., BPF1) can be provided betweenthe antenna and the transmit-receive switch (SW1) such that out-of-bandsignals are ignored. The band-limiting filter (BPF1) can be any filterthat provides reasonable band-limiting functions such as: a passiveband-pass filter, an active band-pass filter, a surface acoustic wave(SAW) filter, a bulk acoustic wave (BAW) filter, a comb filter, astrip-line filter, to name a few.

The PED based locator is operated to receive a transmission from the MTthat consists of another series of coded signals. The coded signal issimilarly generated by the MT with a unique identifier (e.g., the IDCode) that is associated with the specific MT. The receiver block isarranged to receive carrier modulated (e.g., multi-phase shift keying,binary phase shift keying, quadrature phase shift keying, differentialphase shift keying, continuous phase modulation, multiple amplitude andphase shift keying, etc.) coded signals from the antenna (ANT1) via SW1.The received signals are handled by a baseband processor that can alsoprovide signal-processing functions. Alternatively, the basebandprocessor is arranged to provide captured signals to the processor,which is arranged to handle various signal-processing functions.

The described PED based locator performs distance measurement by roundtrip time measurement. For example, the round trip time can bedetermined by the difference in time between the transmission of asignal from the MT to the PED, and the subsequent reply transmission ofan acknowledgement signal from the PED back to the MT, offset by anyother delays.

Bearing to the MT is determined by the operation of the PED in a searchand locate mode as will be described later. In general, the userinitiates a search mode to acquire a communication link and an initialdistance calculation, followed by user initiated movement of the PEDitself. In some examples, the PED is partial rotated through an arcrelative to the user where additional distance and correlatorinformation is evaluated to determine direction. In some other examples,the PED is moved either linearly or non-linearly during distance andcorrelation calculations.

Various timing signals that are employed by the PED in the softwareconfigured two-way radio set are generated by a time control circuit asillustrated in FIG. 6A. The timing signals are used by the system todigitally synthesize transmitter and receiver carrier wave signals froma locally generated oscillator signal in the PED.

Example Micro-Transponder (MT)

FIG. 6B illustrates an example MT (620) that is arranged to communicatewith a PED based locator (610). The example MT (620) may be placed in awristband, a collar, a watch, sewn into an article of clothing, orimplanted in a patient such as a with a bionic-type device. The MT (620)is arranged to receive a coded transmission signal, such as previouslydescribed, from the PED with a receiver block via switch SW2 and antennaANT2. Optionally, a band-limiting filter (e.g., BPF2) can be used tominimize interference from out-of-band signals in the receiver and/or toprevent interference with other devices. The receiver demodulates thecarrier frequency and provides I and Q information, which issubsequently captured by a capture buffer. The capture buffer providesoutput signals in the form of data to an FFT correlator, whichcorrelates the decoded transmission with the unique identifier (IDcode). The processor is arranged to cooperate with memory similar tothat previously described for the PED.

Various processing methods are employed to perform base-band processingand signal analysis in the MT, including a correlator block and a signalanalyzer block. The correlator block may include an FFT correlator and adirect-form correlator. The signal analyzer is arranged to evaluate theoutputs from the FFT correlator and/or the direct form correlator, todetermine if the received transmission sequence is identified with thespecific MT. When the sequence is appropriately identified, varioustiming signals are adjusted such that the frequency and phase of thedigitally synthesized transmitter and receiver signal(s) are preciselyaligned in the MT. Information from the coded signals is extracted bythe processor once the transmission sequence is validated. Suchinformation can include command and control instructions for the MT suchas, for example, set sleep interval to a new time lapse (e.g., 10minutes), log receiver signal strength, log invalid received signals,log receiver frequency and phase, transmit logged data, change to slowping mode, change to fast ping mode, etc.

It is important to note that the processor in the MT (620) of thepresent disclosure is arranged to apply mode control logic in responseto signals that are received from the PED based locator (610). The modecontrol logic an any related settings for the MT (620) can be providedin any of the above described memory devices, or as hard-codedinstructions in a micro-controller, to name a few. In another example,the processor and memory can be replaced with any other appropriateprocessor means such as a PLD, a specially designed circuit such as anASIC, as well as others devices that are arranged to provide similarfunctionality.

A reply message is transmitted from the MT to the PED based locator suchthat the PED based locator can identify, locate, and receive data fromthe MT. The reply message is generated with a reply sequence generatorthat is keyed from the unique identifier (ID Code), similar to thetransmit sequence generator. A low pass filter (e.g., LPF2) can beplaced between the sequence generator and the transmitter block in theMT. The transmitter block is coupled to antenna ANT2 via switch SW2 tocause the coded reply transmission (e.g., COM31, COM32).

Since an example MT operates with limited energy, the MT is normallyoperated in a low power or sleep mode. The energy consumed in the sleepmode is sufficient to operate a sleep timer that operates from a lowfrequency clock. According to a pre-determined time interval, the MT isactivated (e.g., wakeup is asserted by the sleep timer) and the MT looksfor a signal to receive while operating a high frequency clock. When noidentifiable signal can be received, the MT returns to the sleep mode,where the high frequency clock is disabled. The high frequency clock canbe enabled and disabled by a respective control signal (e.g., HF EN).

Various timing signals that are employed by the MT (or MT) are generatedby a time control circuit as illustrated in FIG. 6B. The processor isoperated from one clock signal (CLK2), while the transmitter andreceiver in the MT are operated by other clock signals (TCLK2 andRCLK2). The various timing signals are used by the system to digitallysynthesize transmitter and receiver carrier wave signals from a locallygenerated oscillator signal in the MT.

The time control circuit can include additional functionality tocalibrate the high frequency clock with a calibration logic circuit. Thecalibration logic circuit can include any number of high frequencycounters (HF CNTR), low frequency counters (LF CNTR), and digitalcomparator circuits (COMP), as well as other logic circuits such asregisters, latches and related logic. In operation the calibration logicis enabled when a calibration signal (CAL) is asserted, such as inresponse to the processor when applying mode control logic.

The above described PED based locator can be arranged to provide arelatively high power transmission signal (e.g., 1 Watt) over a longtime interval (e.g., 2.5 seconds) to ensure that the MT has sufficienttime to capture the necessary signals when it is active. The upper limitfor energy that can be captured by the MT is determined by the radiatedpower from the PED based locator multiplied times the capture timeinterval for the MT, multiplied times any loss factor due to thetransmission path. An example transponder (MT) may be arranged tocapture the signal from the PED for 157 μs, where the upper limit(ignoring path loss) for captured energy over the 157 μs time intervalis approximately 157 Pules.

The MT can be arranged to transmit a very low power transmission signal(e.g., 10 mW) for a shorter time interval (e.g., 15.7 ms) than that forthe PED (e.g., 2.5 s). The upper limit for energy that can be capturedby the PED is determined by the radiated power from the MT multipliedtimes the capture time interval for the PED, multiplied times any lossfactor due to the transmission path. For a 10 mW transmission over a15.7 milli-second interval, the transmitted energy from the MT isapproximately 157 Pules. The PED must be carefully arranged to capturesignals form the MT such as by using an integration method as will bedescribed later. It is contemplated that in one example embodiment, theMT will be implanted in a patient, and operated over at least severalyears using a watch-type battery.

The transponder (MT) is arranged to synthesize its own internalfrequency for transmitting an acknowledgement signal by using the timinginformation that it acquires from the PED. The timing information thatis received from the PED by the MT is Doppler shifted relative to theoriginal transmission frequencies from the PED. The resultingsynthesized frequency of the MT, while extremely accurate, correspondsto a Doppler shifted version of the original transmission frequenciesform the PED. The acknowledgment signal from the MT is received by thePED, but is again Doppler shifted relative to the transmittingfrequencies from the MT. The Doppler shift that result from the roundtrip of the signal transmissions (i.e., transmission from the PED to theMT, and reply transmission from the MT to the PED) is hereinafterreferred to as the synthetic round-trip Doppler Shift.

Example Transmitter

FIG. 7 illustrates an example transmitter system. The transmitter systemincludes a crystal oscillator (XTAL OSC), a timing control circuit, acomplex modulator, a pattern generator, an interpolation filter withtiming control, integrators, and a complex cordic rotator.

The crystal oscillator is arranged to provide an oscillator signal as aclock signal (CLOCK) having a first phase (φ₁) for the timing controlcircuit. In one example the crystal oscillator has a nominal frequencyaround 26.14 MHz, which can optionally be adjustable (e.g., via signalFREQ. TRIM). The oscillator can be a crystal-type oscillator, or anyother oscillator that has a substantially stable oscillation frequency.

The timing control circuit includes a feedback control loop with anoptional divider circuit that is arranged to synthesize a frequency. Thecontrol loop includes a phase detector, a low pass filter (LPF), avoltage controlled oscillator (VCO), and an optional divider circuit.The phase (φ) of the reference clock signal (e.g., CLOCK_(REF)) iscompared to a phase (φ₂) from a feedback signal (e.g., CLOCK′) by thephase detector to determine if the resulting clocks signal (CLOCK) isoperating in phase with the reference clock (CLOCK_(REF)). The output ofthe phase detector corresponds to a phase difference signal (φ_(DIFF)),which is provided to the low pass filter to generate a control voltage(VTUNE) for the VCO. The VCO adjusts the output frequency of clocksignals CLKP and CLKN, which are out of phase with one another by 180degrees. The feedback signal (CLOCK) is also provided from the VCO tothe optional divider circuit. The output of the divider circuit isprovided to the phase detector as signal CLOCK′, which closes thecontrol loop. Moreover, the VCO frequency can optionally be provided toanother divider circuit, which generates synthesized frequencies thatare associated with a sine and cosine function.

In one example, the VCO has a nominal output frequency of 1.83 GHz, thefeedback loop divider circuit has a divide ratio of 70, and the phasedetector is arranged to adjust the VTUNE signal via the low pass filtersuch that the average value of the 26.14 MHz signal is matched to 1.83GHz/70. Other reference signals can be employed to yield the same resultby adjusting the divider ratio in the control loop divider circuit.Moreover, the output of the VCO can be further adjusted by the outputdivider circuit (e.g., divide ratio of 2) to yield synthesizedfrequencies corresponding to SIN(915 MHz) and COS(915 MHZ) or any otherdesired frequency.

The pattern generator includes a code control block and a pseudo-noisegenerator block. The code control block is arranged to provide thepre-determined patterns, keyed from an ID Code, for “A”, “B”, and “C”sequenced patterns as will be described later. The pseudo-noisegenerator generates complex numbers (e.g., I and Q) from the codes basedon the timing signals (pattern timing) for sequencing the pattern. Inone example, the pseudo noise generator block is arranged to provide2047 complex numbers. The complex sequence (I and Q) is provided to aninterpolation filter and timing control block, which is arranged toadjust the fine timing associated with the I and Q signals, and providesI′ and Q′, which are associated with a complex interpolated basebandsignal. An integrator circuit is used to integrate the differencebetween the transmitted and received frequencies to adjust the finetiming (fine timing adjust). The interpolator provides fine timingadjustment for the I and Q complex numbers (e.g., 8192/2047), andprovides low-pass filtering for the transmitter. The integrator circuitcan be initialized by an initialization parameter such as f_(INIT)and/or φ_(INIT).

The interpolated complex baseband signals (I′ and Q′) are provided tothe cordic rotator. The cordic rotator adjusts the rotational phase ofthe complex baseband signals (in the digital domain) in response to aphase adjustment signal (e.g., rotation phase). The phase adjustmentsignal is provided by another integrator that integrates the frequencyoffset. The integrator circuit can again be initialized by aninitialization parameter such as f_(INIT) and/or φ_(INIT). The output ofthe complex cordic rotator is a frequency shifted complex basebandsignal (I″ and Q″), where the frequency shifting is undertaken by thedigital synthesis operations by the interpolation filter and the cordicrotator.

The complex modulator is arranged to receive the frequency shiftedcomplex baseband signals (I″ and Q″), and the sine and cosine timingsignals to provide a modulated signal output. The modulated signaloutput can be provided to a power amplifier (not shown) that is coupledto an antenna for transmission of the modulated signal. The varioustiming control signals (e.g., clock frequency, clock phase, clockoffset) are adjusted such that the rate, fine-timing, and phase of themodulated signal output has sufficient timing information embedded inthe resulting signal.

The code control is based on a unique identifier (ID Code). In oneexample, the unique identifier is provided to a polynomial generator. Inanother example, the unique identifier is stored in a volatile memory.In yet another example, the unique identifier is stored in anon-volatile storage such as a flash memory device, a ROM, an EPROM, anEEPROM, a dip-switch, or some other means. In still another example, thepattern that was created with the ID code is stored in a memory deviceor a look-up table instead of the unique identifier.

Example Transmission Sequence

FIG. 8 is a diagram illustrating a set of frames formatted fortransmission. A frame corresponds to a time-period for which a sequenceis transmitted. For the example of FIG. 8, transmissions are broken intothree sequential frames. During a first time-period, a first frame(i.e., “frame 1”) is transmitted that consists of a first transmissionsequence (i.e., “sequence A”). Sequence A consists of a repeated set ofpatterns that are in a sequential series, where each pattern (pattern A)is substantially identical. During a second time-period, a second frame(i.e., “frame 2”) is transmitted that consists of a second transmissionsequence (i.e., “sequence B”). Sequence B consists of a repeated set ofpatterns that are in a sequential series, where each subsequent patternin the sequence is shifted as will be described later. During a thirdtime-period, a third frame (i.e., “frame 3”) is transmitted thatconsists of a third transmission sequence (i.e., “sequence C”). SequenceC consists of a repeated set of patterns, where each pattern (pattern“C”) forms part of an encoded message as will be described later. Thecollection of the three sequential frames in a transmission is referredto as a PING as will be described later.

Each MT in the system has a unique identifier (e.g., an M-bit address)that is used to uniquely designate a specific MT. In one example, theunique identifier is a 33-bit address code that yields approximately8.58 billion unique identifiers. The M-bit address can be dispersed overthe various patterns. In one example, a 33 bit code is evenly dispersedover the three sequences such that 11-bits are coded in “sequence A”,11-bits are coded in “sequence B”, and 11-bits are coded in “sequenceC”. In another example, the codes are not evenly dispersed over thetransmission sequence. In still another example, the same code is usedfor each of the patterns. Each symbol that is transmitted is thusencoded according to the respective coding bits for the correspondingsequence portion. The terms “baud” and “chip” can also be used to referto symbols.

The correlation of sequence “A” is used to verify that the first portion(e.g., the first 11-bits or bits 0-10) of the unique identifier is codedin the transmission. When a correlation is detected, fine baud andcarrier timing can be derived. However, the MT has no prior timinginformation (e.g., no gross frame timing is known). Since the “A”pattern is repeated over the first-time interval, it is possible toaccumulate the signals by adding them on top of one another beforecorrelation is performed such that signal sensitivity is improved. Inone example MT, the accumulation of signals is unnecessary. In anotherexample MT, the accumulation of signals is performed during a repetitivetracking mode.

Once the “A” pattern has been acquired, the MT continues sampling tolocate the “B” sequence. The correlation of sequence “B” is used toverify that the second portion (e.g., e.g., the second 11-bits or bits11-21) of the unique identifier is coded in the transmission. Aspreviously described, the “B” sequence is shifted over time. Forexample, a first B sequence includes coded bauds B0, B1, . . . , BM,while the second B sequence (B′) includes coded bauds B1, B2, . . . ,BM, B0. When correlation is achieved with the MT's “B” sequence, the MTidentifies a stream position within the “B” sequence. Once thetransmission stream position is determined from the shift pattern, theMT schedules the reception of sequence “C”, whose arrival can now bepredicted.

For the above described “B” sequencing example, a single baud shift isused between subsequent transmissions. Other shifting methods can beused such that the step size for shifting between subsequenttransmissions can be a different integer number of baud shifts (e.g., 2,3, 4, etc.) or a non-integer number of baud shifts (e.g., ½ baud, ¾baud, 1½ baud, 2¼ baud, etc.), or a shift in samples of either aninteger or non-integer variety. In another example, the shiftingmechanisms between subsequent transmission can be replaced by a carrierphase rotation, where each subsequent transmission has the carrier phaserotated by a fixed amount.

Frame “C” has a third portion of the unique identifier encoded therein,and possible command and control data for the MT (or other data for thePED). The correlation of sequence “C” is used to verify the thirdportion (e.g., the third 11-bits or bits 22-33) of the unique identifieris coded in the transmission. The “C” sequence can also be very slowlymodulated with a few bits of data. For example, up to 63 bits of dataand error correction code (ECC) can be transferred in sequence “C”. Inone example, the chips or transmit symbols are encoded by inverting ornot-inverting patterns of “C” in the transmission frame. Examples ofcoded command and control information were previously described above.

For the above described “C” sequence, data is encoded using an invertingand non-inverting encoding method. Other data encoding methods can beused such as encoding the data with a shifting bit pattern similar tothe “B” sequence. For example, a “000” binary code can be encoded, andeach increment in the binary code is the same pattern shifted by anincremental shift step (e.g., ½ baud step, 1 baud step, 2 baud step,etc.). The data message nominally in “C” can be encoded with a patterntiming changes as in the nominal section “B” previously described.

The MT transmits sequences A and B in substantially the same format asthat described above. However, since the PED initiated the transmissionand does not have a “wake-up” period creating an ambiguity in whenreception begins, the transmission sequence from the MT can be shorteroverall. The shortened transmission period helps minimize the MT'senergy consumption. Frame “C” is similarly formatted, but may includeother reported data such as: current temperature, heart rate, bloodpressure, etc.

The timing and carrier signals for transmission in the MT are derivedfrom the PED's synthesized clock as measured against the internal MTclock. The PED in turn correlates these signals, similar to the MT, anddetermines the exact round-trip time. The PED also determines deviationsin the signal timing with respect to its own clock, which the MTattempted to mimic. The deviation in the signal timing is a consequenceof Doppler shift, noise, and oscillator instability.

An example system has the following general information:

-   -   Received Frame consists of 4096 samples, 2047 baud;    -   Received Sample Rate is 25.777 M complex samples/sec;    -   Transmitted Sample Rate is 2*25.777 M complex samples/sec;    -   Baud Rate is determined by Sample Rate*(2047/2048)/2=12.8822        Mbaud symbols/sec, QPSK; and    -   Frame Period is 158.98 μs.

An example system has the following PED TX parameters:

-   -   “A” sequence is 2.2263 seconds long, (13×1024 frames), repeated        un-shifted with one of 2047 first address portions;    -   “B” sequence is 317.96 ms long (2000 frames), repeated shifted        with one of 2047 second address portions; and    -   “C” sequence is 10.174 ms long (64 frames), repeated un-shifted        with one of 2047 third address portions, frames inverted        according to modulated data.

An example system has the following MT TX parameters:

-   -   “A” sequence is 81.397 ms long, (512 frames);    -   “B” sequence is 20.349 ms long (128 frames); and    -   “C” sequence is 10.174 ms long (64 frames), repeated un-shifted        with one of 2047 third address portions, frames inverted        according to modulated data.

Example Timing Acquisition Sequence

FIGS. 9A and 9B are diagrams illustrating the timing acquisition for anexample communication system. The described timing acquisition sequencemay be employed by the MT when receiving the three-part transmissionsequence described previously with respect to FIGS. 1A, 1B, 2 and 3.However, as described herein, the timing acquisition sequence can beaccomplished with only two of the three portions of the transmissionsequence (e.g., sequence A and sequence B).

The receiver frequency is digitally synthesized from a locally generatedclock circuit (e.g., a crystal oscillator). The carrier wave from thePED is also digitally synthesized from its own locally generatedclocking circuits, and will likely be mismatched from the receiverfrequency in the MT. The mismatch may be related to thermal differencesin the operating environment, heat transients in the circuits, crystaltolerances, processing differences between the MT and the PED, as wellas other non-ideal effects. Moreover, the overall system is notsynchronized so there is no way to initially know the starting phase,frequency and cadence associated with the transmissions. FIG. 9Aillustrates examples of phase and frequency determinations associatedwith an example “pattern A” sequence, while FIG. 9B illustrates theuncertainty in the receiver frequency over time during the timingacquisition.

The receiver portion of the communication system is initialized at timet₁ to an initial frequency (f) that is designated as f=f₀. However, theoffset between the digitally synthesized receiver frequency and thecarrier frequency from the received transmission is unknown at timet=t₁. The MT is arranged to measure the phase associated with thereceived signals from pattern A as phase φ₁. The phase measurement(e.g., φ₁) can be generated by an output of the correlator.

At time t=t₂, another portion of the transmission of pattern A isreceived, and the MT is arranged to measure the phase as φ₂, andcalculate a frequency offset error associated with the differencebetween the expected receiver frequency and the actual carrier wave fromthe PED's transmission. The frequency offset (f_(offset2)) is determinedby the difference in the phases and the elapsed time between as:f_(offset2)=[φ₂−φ_(ex2)]/[360(t₂−t₁)], where φ_(ex2) corresponds to theexpected phase at time t₂. It is important to note that the time betweenthe first two measurements should be short enough to result in anexpected relative phase difference of substantially less than 180degrees to ensure that unresolveable ambiguities do not occur. Noticethat the expected phase for this time corresponds to φ₁.

At time t=t₃, another portion of the transmission of pattern A isreceived, and the MT is arranged to measure the phase as φ₃, andcalculate a frequency offset error associated with the differencebetween the expected receiver frequency and the actual carrier wave fromthe PED's transmission. The frequency offset (f_(offtet3)) is determinedby the difference in the phases and the elapsed time betweentransmissions as: f_(offset2)=[φ₃−φ_(ex3)]/[360(t₃−t₂)], where φ_(ex3)corresponds to the expected phase at time t₃. It is important to notethat the elapsed time for the first two measurements should again resultin an expected relative phase difference of substantially less than 180degrees to ensure that unresolveable ambiguities do not occur. However,the absolute phase difference is expected to be significantly largerthan 360 degrees such that the time difference between successive offsetcalculations can be gradually spaced further and further apart as thetiming acquisition is adjusted by each subsequent estimate. Notice thatthe frequency error is gradually reduced with each subsequent adjustmentuntil limited by the Allan Variance.

FIG. 9B is a graph illustrating the uncertainty in the digitallysynthesized receiver frequency over an elapsed timing acquisitionperiod. Note that the scale for both axes is logarithmic, and that theuncertainty will asymptotically approach the Allan Variance associatedwith the crystal oscillators in the MT and the PED. The horizontal axisillustrates elapsed time, while the vertical axis illustrates theuncertainty in the frequency. Each successive time period has a refinedestimate of the receiver timing such that the uncertainty decreases inan exponential fashion. A knee in the uncertainty curve occurs aftersufficient samples of the received signal are acquired (e.g., at timet₅) such that estimates for the received carrier wave frequencyasymptotically approach a minimum uncertainty that is determined by theAllan variance.

Example Receiver

FIG. 10A is a block diagram for an example receiver. The examplereceiver includes an antenna (ANT), an optional filter, a low noiseamplifier (LNA), a first mixer, a second mixer, a first low pass filter(LPF1), a second low pass filter (LPF2), an analog-to-digital converter(ADC), a buffer, an FFT processor, a correlator, and an inverse FFTprocessor. Other example receivers can use an analog storage method andperform a delayed A/D conversion.

The antenna is arranged to couple received signals to the LNA throughthe optional filter (e.g., a band-pass filter). The LNA is arranged toincrease signal strength, and couple the increased signal to the mixers.The first mixer is arranged to generate an in-phase signal (I) with acosine wave heterodyne, while the second mixer is arranged to generatequadrature signal (Q) with a sine wave heterodyne. The in-phase signalis coupled to the ADC via LPF1 as signal I_(A), while thequadrature-phase signal is coupled to the ADC via LPF2 as signal Q_(A).

The ADC is operated at a sampling frequency (f_(SAM)). The ADC can beimplemented as a single A/D converter circuit with time divisionmultiplexing between the I_(A) and Q_(A) signals. The ADC canalternatively be implemented as two separate A/D converter circuits. TheADC circuits convert the I_(A) and Q_(A) signals to quantized digitalsignals that are coupled to the buffer as signals I_(D) and Q_(D),respectively. The buffer can be implemented as one contiguous memory, aspartitioned memory (e.g., MEM1, MEM2, etc.), or any other appropriatetemporary storage that buffers the captured data.

The output of the buffer is coupled to the FFT processor, which convertsthe input signal to the frequency domain. The FFT of the referencesignal is complex conjugate multiplied with the frequency domainrepresentation of the captured signal. An inverse FFT of the product istaken, which is the circular correlation of the captured signal and theselected reference signal. Since the FFT reference is determined fromthe unique identifier of a MT (e.g., ID Code), the correlation of theFFT processor output will peak when a valid received code is identifiedin the signal. The carrier phase and pattern timing are also extractedfrom the received signals.

FIG. 10B illustrates operations in a receiver that may be performed as aDSP block. The FFT reference signal is provided as an array of N-bins.The captured signal is calculated as an FFT, also of N bins. Next, thecomplex conjugate of each complex element in a designated storage bin(BIN 1-BIN N) is multiplied by the data from the other correspondingstorage bin. For example, the complex conjugate of the FFT referencesignal is stored in a first array (ARRAY 1) as D_(RI)-D_(RN), and theFFT capture data is stored in a second array (ARRAY 2) as D_(C1)-D_(CN).In another example, the FFT reference signal is stored in the firstarray (ARRAY 1) as D_(RI)-D_(RN), and the complex conjugate of the FFTcapture data is stored in the second array (ARRAY 2) as D_(C1)-D_(CN).

The multipliers are arranged to receive data from the first array andthe second array to provide a multiplied output, yielding a productresult that can be stored in a third array (ARRAY 3) as D_(M1)-D_(MN).An inverse FFT is computed from the product identified in the thirdarray (ARRAY 3), to retrieve the circular correlator output. Thecircular correlator output results can be stored in a fourth array(ARRAY 4), or can optionally overwrite the values from the third array(ARRAY 3). The contents of the fourth array (ARRAY 4), or the thirdarray depending on the implementation, are a complex result thatincludes both magnitudes and phases. As illustrated in FIG. 5B, theinverse FFT of the circular correlator output has a peak magnitude(PEAK) that occurs when the FFT reference ad the captured data correlatewith one another. Each bin (BIN1-BIN N) of the third array (ARRAY 3), orfourth array depending on the implementation, corresponds to the outputof the correlator, wherein a PEAK may be located in one of the bins(e.g., BINX), when a correlation occurs.

Example Operational Flows for Transmission and Reception

FIG. 11 is a flow chart for an example transmitter configuration ineither a MT or a PED based locator. Processing begins when a user, orsome other process, initiates a request to locate a particular MT.

A transmission sequence is initialized with a unique identifier (IDCode). Sequences are generated for frame transmission such as sequence“A”, “B”, and “C” as previously described. Each of the “A”, “B”, and “C”sequences consists of bauds that are encoded with a portion of theunique code.

Next, the PED (or MT) then begins transmitting pattern “A”, and repeatstransmitting pattern “A” (Note: un-shifted) until the entire “A”sequence is completed (e.g., 13×1024 sequential patterns, or frame “A”).The PED then begins transmitting pattern “B”. For each subsequenttransmission of pattern “B”, the pattern is shifted such as using a bitrotation algorithm, as previously described. After the entire sequenceof “B” patterns is transmitted (e.g., 2000 sequential patterns, or frame“B”), the PED begins transmitting the “C” pattern. The sequence of “C”patterns includes modulated data that may correspond to command andcontrol information for the MT. After the modulated data is transmitted(e.g., 64 sequential pattern, or frame “C”), the PED stops transmittingand switches into a receive mode.

In the receive mode, signals are received from the MT with the PED in asimilar format as provided between the PED and the MT. The PED can thencalculate a distance and location based on the round-trip time andDoppler shift in the received signals as previously described. Moreover,the received “C” frame transmission may include data that iscommunicated between the MT and the PED, which is extracted andevaluated by the PED. Such data may include: physiological informationsuch as heart rate, body temperature, blood pressure, heart rhythm,blood-sugar level, as well as other sensory information that isassociated with a user of the MT.

FIG. 12A is an example flow chart for an example receiver in a MT.Processing begins when the MT is activated out of a sleep mode (e.g.,WAKE-UP is initiated). FIG. 12A illustrates the capture of samplesassociated with sequence “A” (or frame “A”). After wake-up is initiated,the receiver captures noise and/or signals. The MT will attempt tocorrelate the captured noise and/or signals with the first portion ofthe unique identifier for the specific MT. When the correlation fails tomatch, the MT determines that the transmission is intended for anotherdevice, or possibly that no transmission is present, and returns to asleep mode. Alternatively, the MT extracts baud and carrier timinginformation from the transmission sequence to refine the receivertimings.

Timing is refined by repeatedly scheduling capture intervals. Thereceiver waits, and then begins capturing a portion of the samples fromeach scheduled capture time, and attempts to correlate the capturedsamples with another portion of the reference that is keyed to the codefor the MT. Each time the correlation indicates a match, the timing forthe receiver is adjusted (bootstrapped) to further refine thetime/frequency estimates. Eventually, the correlation of pattern A failsto match the coded reference and processing continues to capture andevaluate pattern B as will be described with respect to FIG. 13A.

FIG. 7B illustrates the capture of samples associated with sequence “A”(or frame “A”) in a receiver of an example PED device. Since the MT haslimited power available for transmission, the signal may be considerablyweaker than that from the PED. After wake-up is initiated by the PED,the receiver captures noise and/or signals. The PED will continue tocapture the transmission for a predetermined time interval andaccumulate values using a cyclic accumulation capture technique (e.g.,an array of capture buffers that are cyclically selected in sequence).For each subsequent capture, the selected capture buffer is changedbased on the time. Also, an accelerometer is used to measure the speedof the PED device for estimating time for reception, etc.

After the predetermined time interval expires; the PED attempts to FFTcorrelate the accumulated/captured signals and noise with the firstportion of the unique identifier for the specific PED. The accumulationof the captured patterns over the sequence using the described cyclicaccumulation improves the signal levels and minimizes the impact ofnoise on the reception. When the correlation fails to identify a match,the PED determines that the transmission is intended for another device,that no transmission is present, or that an error has occurred, andreturns to a sleep mode. Alternatively, the PED fine timing and phaseinformation from the transmission sequence is used to refine thereceiver timings for the PED. Processing then continues to capture andevaluate pattern B as will be described with respect to FIG. 13B.

FIG. 13A illustrates the capture of samples associated with pattern “B”in a MT device. The receiver captures a sequence of samples, assumingthose samples correspond to sequence “B”. The MT will attempt to FFTcorrelate the captured samples with the second portion of the uniqueidentifier for the specific MT. When the correlation fails to identify amatch, the MT may determine that the signal sequence is intended foranother device. During a processing time interval, the expected Bsequence is shifted and captured, and FFT correlation determinationsthen follow. When the processing time interval completes without a matchof sequence “B”, the MT determines that the transmission is intended foranother MT or that there is no transmission to receive and returns to asleep mode. Alternatively, if the MT finds a match for sequence “B”,then the MT determines the relative position of the matched patternwithin the sequence (or within the frame) based on the shift positionthat yields a match. Since the timing, phase, and frequency informationare now known, the MT schedules reception of the “C” sequence.Processing continues for the MT in FIG. 14, which follows further below.

FIG. 13B illustrates the capture of samples associated with pattern “B”in a PED device. The receiver captures a sequence of complex samples(e.g., 4096 complex samples), assuming those samples correspond tosequence “B” using a cyclic accumulation/integration technique that issimilar to that previously described for FIG. 7B. A reference patternassociated with pattern “B” is generated. Each received sample iscaptured and placed in a respective one of a series of buffers, whereeach buffer has an associated index such as a pointer. Each subsequentlycaptured sample is placed in a different capture buffer (e.g., acapacitive storage cell).

As previously described with respect to the MT, sequence “B” istransmitted multiple times for receipt by the PED, where each subsequent“B” sequence is cyclically rotated with respect to the precedingsequence (e.g., see FIG. 3). As time moves forward a different capturebuffer is used as the starting point for capturing a sequence by thePED. For example, assuming a 4096 complex sample pattern with a startingpointer to capture buffer 0, captures will be placed in buffers 0-4095in sequence. After the first “B” sequence is captured, the next pattern“B” sequence will have a starting point for capture buffer 2, andcaptures are placed in buffers 2-4094 sequentially followed by capturebuffers 0 and 1. Each buffer can be an analog storage cell so thatsamples from the first pattern are accumulated with the samples from thesecond pattern using the described method. After numerous accumulationsof additional patterns, integration is completed and the accumulatedsignal can be evaluated.

After all of the samples for pattern sequence “B” (e.g., 4096 complexsamples from a sequence of pattern “B”) are received (i.e., “patterncomplete”) and accumulated, the PED will attempt to FFT correlate theintegrated captured sequence with the previously generated pattern forpattern “B”. When the FFT correlation fails to identify a match, the PEDfalls into an error trap. Processing a received sequence may expirewithout match when the transmission is intended for another MT, orperhaps when an error has occurred. An error trap handles the remainingprocessing when an error occurs.

When the PED finds a correlation match for the generated pattern “B”,the PED can then determine the relative position of the matched patternwithin the sequence (or within the frame) based on the shift position inthe pattern that yields a match. Since the timing, phase, and frequencyinformation are now known, the PED schedules to receive the “C”sequence. Processing continues for the PED in FIG. 9, which followsbelow.

In some examples systems the “B” sequence is sampled four times at thetransmitter, with each sequence step being four samples. For thisexample, the receiver samples at half the transmit rate so that eachshift in the pattern corresponds to two buffer locations. In otherwords, the starting point for each “B” sequence capture for this examplealways corresponds to an even numbered buffer (e.g., 0, 2, 4, . . . ).The PED can then determine the relative position of the matched patternwithin the sequence or frame by evaluating the starting point index tothe buffer or sample bin that matches or correlates to the expectedpattern.

FIG. 14 illustrates the capture of samples associated with sequence “C”.The receiver captures samples from the receiver in the MT, assumingthose symbols correspond to pattern “C”. The MT will continue to capturesamples until the frame is expected to reach completion. The MT willthen attempt to correlate the captured sequence (assuming it is sequence“C” from the PED) with the third portion of the unique identifier forthe specific MT. When the correlation fails to achieve a sufficientlevel for detecting a match, we can assume as a formality that thetransmission of the “C” sequence has failed for any number of reasons(excessive noise in the environment, a high strength interfering signal,etc.) Since we know precisely when transmission of sequence “C” shouldoccur, and what carrier frequency, phase, timing, and cadence for whichtransmission should occur, the receipt of the “C” pattern can be usedformalistically for verification of a valid transmission.

Sequence “C” includes data modulated therein that may be coded witherror correcting codes (ECC), where the coded information can be phasemodulated and subsequently demodulated and decoded. When the time-periodhas not expired, capturing of the expected C sequence is resumed,followed by correlation determinations again. When the time-period hasexpired without a match of sequence “C”, the MT determines that thetransmission is intended for another and traps an error conditionappropriately. Alternatively, the MT finds a match for pattern “C” andevaluates the polarities of the symbols received in this frame, andextracts command and control information from the “C” sequence.

In the case of the MT, the completed capture of sequence C is followedby a transmission of sequences “A”, “B”, and “C2” (or some other order,perhaps, or even a different set of A′B′C′. Sequences “A” and “B”include a similar pattern as previously described for the PED, althoughshorter in length. Sequence “C2” is still the same number of framesexcept that data is encoded into the transmission for communicationbetween the MT and the PED.

In the case of the PED, the completed capture of sequence C is followedby evaluation of the round-trip time to determine linear distance fromthe PED to the MT. A time difference is evaluated between the receptionof two signals that are received from two different receiving antennasto help identify a vector for direction between the PED and the MT. Ananalysis of a Doppler shift in the received signals from the MT can alsobe used to assist in the determination of the directional vector. Inaddition, sequence “C” is evaluated to extract transferred informationfrom the MT to the PED. Moreover, measurements from the compass sensorand can be utilized to assist in determining location as will bedescribed later.

Example Operational Features and Observations

The present disclosure merges “location request” polling with thelocation process itself. The PED device is arranged to provide arelatively lengthy, powerful, coded signal whose duration spans thepolling interval of the MT. The MT very briefly samples the relevantspectrum, and finds a coded spread spectrum signal. In this event, theMT performs multiple signal captures from the lengthy transmission,making successively more accurate estimates of the signals frequency,cadence, and time reference. These estimates are limited in precision bythe short-term stability (root Allan variance) of the MT's and PED'stime bases (e.g., a quartz crystal oscillator) and by the relativeacceleration between the PED and the MT. This Allan variance willtypically be better than 1 part per billion, but the acceleration forobservation periods of 0.25 seconds may be the order of: 10 meters/sec²by 0.25 seconds, which would give a 2.5 meter/second Doppler change.This lurch is unusual, and typically, a 0.25 meter/second change or lessis observed. A velocity change of 0.25 meter/second round-trip is 0.5meter/second, which is a Doppler change of 0.5/3*10⁸, or 1.6 parts perbillion (ppb). Thus, the estimates of incoming signal frequency/sequenceshould have a precision of approximately two (2) parts per billion orbetter. Experimentally, two (2) ppb has been observed.

The MT can use the precise estimate of the received signal timing tosynthesize a coded spread spectrum reply with substantially the sametiming and carrier frequency. This reply signal is emitted shortly afterthe end of the incoming signal. Since the timing is accurately captured,the presence of a delay or gap doesn't materially degrade accuracy. Forexample, if the time-base error is 2 ppb, then a 30 ms delay translatesinto a time uncertainty of approximately 60 ps, which is about onecentimeter of round trip distance.

The coded reply signal from the MT is sufficiently lengthy so thatintegration over time compensates for its relatively low power. Thesignal from the MT can be coherently processed by the PED since thereturn signal is coherent plus or minus the synthetic round-trip Dopplershift with the PED's time base. A cyclic set of 4096 complex capacitiveintegrators can be used to perform the process of signal accumulation toraise the weak signals up and out of the noise floor. The complexpatterns (e.g., a pattern of length 2047 chips) have approximately 33 dbof spreading gain. The addition of the cyclic integrators can achieve anadditional 20 db of signal gain with the repetitive portions of thesignal, yielding 53 db of total gain. A bandwidth reduction from 26 MHzdown to about 100 Hz is achieved with this technique. The thermal noiseover the 100 Hz bandwidth is approximately −154 dbm, where reasonablesignal reception is expected around a noise level of −140 dbm. A maximumpath loss of 150 dB is achieved for a +10 dbm transmitter. Thecorresponding ideal free space range for this transmitter isapproximately 1000 km assuming a 915 MHz signal and omnidirectionalantennae. This large free space range or loss margin is useful forbuilding penetration, implanted devices, and so forth.

The capture duration in the MT is limited by the relative crystalfrequency tolerance between the MT and the PED. With time andtemperature, and taking advantage of periodic calibration signals, thistolerance can be managed to a few parts per million. Thus, the productof the signaling frequency and the crystal tolerance gives a frequencyoffset, which in turn indicates the maximum possible reception timewithout the use of multiple Doppler bins or repeated correlationattempts. For example at 915 MHz and with a 3.5 ppm frequency error, acapture period of 312 μs would correspond to a first complete signalnull.

The PED will in general receive a signal whose cadence and frequencyvery closely match its internal crystal clock, and thus the PED can uselong cyclic integration times, which greatly increase the availablesignal to noise ratio. The described coherent integration (or coherentaccumulation) process has a signal power maximum when the signal hasrotated through 180 degrees at the end of the capture interval. For a3.5 ppm frequency tolerance, when the period of the spread signal isdesigned to be about 150 μs. It is advantageous to use a signal which isitself complex. Improved orthogonality between coded signals is achievedby using a complex signal. For example, the Gold codes used in the GPSsystem have a length of 1023 chips with a cross correlation ofapproximately −24 db for 1025 possible codes. The complex signalingcodes employed in the presently described disclosure is on the order oflength 2047 chips, with a cross-correlation of −33 db for 2048 possiblecodes. The use of complex codes allows for improved signal rejection.

The round trip Doppler shift between slowly moving objects (e.g., peoplewalking) is on the order of 4-5 ppb. Slowly moving objects provide asignificantly longer integration time in cases where the received signalis likely to be very close in frequency to the PED's time base. Evenautomobile speeds will result in a round-trip Doppler-shift of 200 ppbor less.

Optional PED Compass Operation

The described system performs distance measurement by round trip timemeasurements. According to the present disclosure, an economicalsolution is available for a remote locator (PED) device that does notrequire accelerometers or multiple antennas for resolving directionalinformation. A compass sensor can be adapted for use in the PED suchthat the target direction (the direction towards the MT from the PED)can be continuously displayed despite any relative change in the PED'sorientation. Diversity antennas can be used to gain additionalinformation about signal strength, distance and Doppler, etc.

Initially, when the user of the PED seeks to find an MT, a “search” modeis engaged. When the PED receives a satisfactory counter-signal from theMT the PED can determine the distance to the MT and provide anappropriate alert indicator to the user. Alert indicators may include,for example, an audible indicator via the audio output device, a visibleindicator via the video output device, or a vibrating indicator.

After the initial search and alert are completed, the user can activatea “locate” mode. In the locate mode, the user holds the PED away fromthe body approximately at an arms length. The user then moves the PEDthrough at least a portion of an arc or through a complete circularmotion that is centered approximately about the user's head.) to scanfor the MT. During the locate mode, the PED will handshake many timeswith the MT while acquiring a series of data items such as time ofarrival (TOA), and Doppler readings which are interferometric. As thePED is spun in a circular motion, compass readings are also taken. Thecompass readings are associated with distances and Doppler readings. Thedistance change associated with the rotation is doubled by theround-trip transit time. In one example, a user may extend the PED awayfrom his body around 70 cm of distance, and the corresponding round-triptime variation is around 280 cm, or about 8 waves at a frequency of 915Mhz.

An example user rotates the PED at a variety of rates that can rangebetween around 36 degrees/second and 180 degrees/second. The distancemeasurements that are acquired by the PED will fluctuate based on thePED's relative orientation relative to the MT. In other words, thedistance between the PED and the MT is a function of the rotationalposition of the PED during the circular spin. The distance is also afunction of the distance the user extends his arms to hold the PED awayfrom their body during the rotational movement. In one example, the userholds the PED 70 cm away from their body, the compass reading has aninitial reading of 84 degrees and the actual target is located at aheading of 120 degrees. For this example, the heading difference betweenthe initial reading and the actual target is 34 degrees, which result ina distance change between the actual target and the user of: 20.7 mCOS(34°)=1.1326 m. As the user continues to rotate about theircenterline, the distance to the target continues to change asillustrated by FIG. 10A. When the PED is oriented at the target headingof 120 degrees, the distance change peaks (1.4 m), while the distancechange is lowest (−1.4 m) when the PED is oriented at the heading of 300degrees since the PED is positioned at the furthest point relative tothe target (180 degrees away from the target).

The heading from the PED to the MT is unknown until at least a partialrotation is complete and sufficient data is collected of compassreadings, distance measurements, and Doppler readings to resolve theproper direction. The correlator in the PED is arranged to generatecorrelation phase information heading between the target location (theMT) and the PED. The correlation phase information is illustrated by thegraph of FIG. 10B, where the correlation phase (Phase) is determined bythe following equation: Phase=360° (Φ−Δd/λ), where Φ is the initialcorrelator phase, Δd is the change in distance for a given directionalheading, and λ. is the wavelength of the transmission.

As described, the PED is arranged to collect a series of compassheadings and distances to resolve a target location for the MT. Themotion or action required of the user is relatively intuitive in thatthe circular motion required for the PED is similar to the motionrequired for a user to visually search by “looking around” their currentlocation. The cost of a PED that is employed in the above-describedexamples is reduced considerably since the use of accelerometers is notrequired. Moreover, the cost associated with some conventional two axiscompass sensor devices is currently less than approximately two dollars.

Look Around Procedure

FIGS. 16A-16C are example illustrations for a look-around procedure thatis employed by a user in a search and locate mode arranged according toat least one aspect of the present disclosure. The procedure illustratedby these figures depicts an owner that is searching for their dog, whichhas disappeared in the neighborhood. The dog has a MT device affixed totheir collar, for example, so that the dog can be found with a hand-heldPED device. The description is not intended to be limited to locatinganimals, and can be used to locate any object, person, animal, or thingthat has a transponder device affixed thereto, or perhaps implantedtherein

As illustrated in FIG. 16A, a person comes out of their home to searchfor a runaway dog (e.g., “Winston” the dog) while holding an PED device,which is depicted in this example as a small hand-held device. Theperson activates the PED device into a search mode by pressing one ofthe buttons on the device (see FIG. 16B), and the PED transmits a pingto the MT. If within range, the MT transmits a reply to the PED. Whenthe PED recognizes that the MT has been found, a user alert is issuedsuch as an audible beep or a visible indicator. At this point the personactivates the locate mode by pressing one of the buttons on the device.During the locate mode, the person extends their arm away from theirbody and rotates the PED about their centerline (e.g., see the dottedline in FIG. 11A), such as by pivoting about their heels.

Once a sufficient rotation has been completed the PED has found the MT(aka “Winston” the dog), and a directional indicator is illuminated on adisplay of the PED device as shown in FIG. 16B. Also shown in FIG. 16B,the distance between the PED and the MT is displayed indicating that“Winston” is located 172 feet away towards the right. As shown in FIG.11C, the person then walks in the direction of the arrow on the displayof the PED to locate the dog. As the person approaches the dog, thedistance measurement will be updated to indicate that they are gettingcloser and closer. Once the person is within a close proximity (e.g., 10feet) of the dog, the PED can provide a short audible indicator and thengo to sleep mode.

Ping Modes

FIG. 17 is an example diagram illustrating single ping mode, slow pingmode, and fast ping mode. As previously described a “ping” correspondsto a complete transmission by the PED to the MT, such as a complete setof the three frame transmission sequence. Similarly a “reply”corresponds to a complete set of frames from that are transmitted fromthe MT to the PED. In FIG. 17, each block designated as Px is intendedto indicate a time of transmission for a ping that includes a completeset of frames, while Rx is intended to indicate a time of transmissionfor a reply that also includes a complete set of frames.

The described system performs distance measurement by round trip timemeasurements. The ping modes are arranged to provide regularcommunications between the PED and the MT, where distances can betracked without excess energy consumption or spectral pollution. Afteran MT and PED have exchanged signatures, they share very precise mutualclock rate information. The accuracy of this clock rate information,absent any Doppler shift, is one part per billion or better. As timeelapses between transmissions, the unit time bases, which aren'tperfectly steady, will drift with respect to each other. By calibratingthe low-speed sleep mode oscillator against the high-speed clock, sothat a given sleep period can be accurately enumerated as a known numberof high-speed clock periods, it is possible to accurately measureperiods of several minutes without actually operating the high-speedclock. However, a long initial baseline for frequency determination isnecessary to initially synchronize the clocks between the MT and thePED. Once synchronized/calibrated the precise timing is known andshorter transmissions are possible.

In the single ping mode, the PED transmits a single ping (P1) to the MT.The MT receives ping P1 when it within a transmission range of the PEDfor proper reception. The MT is arranged to transmit a reply (R1) to thePED in response to ping P1 when the ping is properly recognized as codedfor the particular MT.

In the slow ping mode, the PED is arranged to continuously transmit aseries of single pings (P1′, P2′ . . . PN′) to the MT. Each subsequentping is separated in time by a ping interval (T1) as illustrated. The MTreceives each ping when it is located within a transmission range of thePED for proper reception, and transmits a corresponding reply (R1′, R2′. . . RN) for each ping that is properly recognized as coded for theparticular MT.

In the fast ping mode, the PED is arranged to continuously transmit aseries of short duration single pings (P1″, P2″ . . . PN″) to the MT.Each subsequent ping is separated in time by a ping interval (T2), whichis significantly shorter in time than ping interval T1. For example,each ping in the fast ping mode is on the order of hundreds ofmicroseconds to a few milliseconds in length. Since the timing andcadence is know from prior receptions, the coarse timing is alreadyknown and the PED is able to utilize greatly abbreviated transmissions.The short duration ping can be accomplished using just a portion of an“A” sequence. The MT receives each ping when it is located within atransmission range of the PED for proper reception, and transmits acorresponding reply (R1′, R2′ . . . RN′) for each ping that is properlyrecognized as coded for the particular MT.

It is important to note that the MT may not always be able to properlyreceive a particular ping from an PED in even though it is properlycoded for recognition by the MT. Environmental conditions such as noise,buildings, and other electronic interferences may inhibit a ping (e.g.,ping P2′) from reaching the intended MT. Similarly, environmentalconditions may cause a reply (e.g., reply R3″) from reaching theintended PED.

Example Operation of the PED in Search and Locate Modes

FIGS. 18A-18D are example flow charts for example mode selectionfeatures for an example remote locator (PED) arranged according to atleast one aspect of the present disclosure.

Initially, a user input is asserted to activate the search mode on thePED, such as by activation of a button shown as shown in FIG. 16B or viaa speech input as previous described. The user input is evaluated by themode logic in the PED to decide if the user is requesting the searchmode. The search mode can be implemented as a single ping mode or amultiple ping mode.

As described in FIG. 18A, a single ping is transmitted from the PED tothe MT (e.g., P1 from FIG. 17) when the single ping mode is selected bythe user for the search mode. The PED then waits to detect a reply fromthe MT (e.g., R1 from FIG. 17). If no reply is detected, the PED deviceactivates a sleep mode to conserve power. When a reply is properlydetected from the MT, the PED measures the distance to the MT based onthe round-trip time of the ping and the corresponding reply. Indicatorson the PED are updated to alert the user of the currently determineddistance. Example indicators include an LCD display that indicates thecurrent distance, an audible indicator, a vibrating indicator, as wellas others. The PED then waits for another user initiated input to changefrom the search mode to the locate mode. The locate mode requires a fastping sequence as will be described with reference to FIG. 18B.Otherwise, another mode can be selected or the device can go to a sleepmode to conserve power.

Referring now to FIG. 18B, a fast ping mode is activated by the PED thenuser selects the locate mode. During the locate mode, the user initiatesa spin around procedure such as that previously described, and the PEDtransmit pings at a more frequent interval such as illustrated by timeinterval T2 in FIG. 17. After each ping is transmitted by the PED,compass readings are captured and the PED looks for a reply from the MT.A timeout detection and error trap procedure can be employed to takeappropriate action (e.g., go to sleep mode) when the MT does not replywithin a prescribed time limit. Otherwise, each reply from the MT isanalyzed to determine distance and phase information as the spin aroundis initiated. The compass readings are analyzed with the calculateddistances to determine if an initial location for the target has beenidentified. As previously described with reference to FIGS. 15A and 15B,the calculated distance will change as the user initiates thespin-around such that a minimum distance can be identified when the PEDis oriented at a closest point towards the MT. The captured data can befurther analyzed to ensure an accurate reading on the compass. The PEDincludes updates direction indicators for based on the identifiedinitial location as illustrated in FIG. 16, where a compass isilluminated to identify the heading to the target and an LCD displayindicates the range to the target. Once the user has located the target,the slow ping mode is activated (see FIG. 17) and processing continuesto FIG. 18C.

As shown in FIG. 18C, the user can begin walking towards the MT afterthe initial location is identified. The PED transmits a slow ping, whereeach subsequent ping is spaced apart in time such as is illustrated bytime interval T1 in FIG. 17. Compass readings are captured and thedistance measurements and current direction indicators are updated eachtime a reply is received from the MT. The desired direction to locatethe MT is also indicated on the PED so that the user can monitor if theyare walking in the proper direction or not. Once the PED is within aprescribed range such as 10 feet, for example, the PED provides an alertindication (e.g., a sound, a flashing light, a vibrating alert, etc.)that the target has been found and the PED goes to a sleep mode. Atimeout detection and sleep mode activation can be employed for caseswhere the PED loses communication with the MT once the slow ping mode isenabled.

When a mode other than the single ping mode is selected by a user fromFIG. 18A, processing continues to FIG. 18D. A continuous ping mode canbe activated by the user for the search mode, where a slow ping isperiodically transmitted from the PED to the MT. Distances arecalculated and compass readings are captured when the PED detects areply from the MT. Distance indicators are then updated on the PED(e.g., range readings are updated, lights are activated, sounds areinitiated, etc.). User inputs are evaluated during the continuous pingmode to permit selection of any number of modes such as a sleep mode oractivation of the locate mode such as described above with reference toFIG. 18B. When replies are not received from the MT with a prescribedtimeout period, the device can again go to a sleep mode to conservepower. Other example modes can include bookkeeping modes were data andother diagnostic information can be collected by the PED, or perhaps thePED can transmit a command for the MT to log or transmit otherinformation.

Example Operation of the MT in Search and Locate Modes

FIGS. 19A-19B are example flow charts for example mode selection in anexample micro-transponder (MT) arranged in accordance with at least oneaspect of present disclosure.

As shown in FIG. 19A, the transponder is initially in a slow ping modesuch as described previously. When a ping is detected from the PED, theMT transmits a reply to the PED and evaluates any coded messages orcommands that are communicated in the ping. When the PED requests the MTto change modes, processing continues to FIG. 19B.

The change mode request is evaluated by the MT in FIG. 19B. The moderequest may be to change to a fast ping mode, enter a bookkeeping mode,or some other mode as may be desired. In the fast ping mode, the MTmonitors received signals more frequently than the slow ping mode andprovides a rapid reply to the PED. In the bookkeeping mode, the MTencodes additional information into reply messages for the PED such as,for example, estimated battery life, environmental sensor data such asambient temperature and pressure, biological sensor data such as heartrate and blood pressure, receiver signal quality, receiver signalstrength, etc. Eventually, the PED will transmit a signal to changemodes back to slow ping mode and the processing will return back to FIG.19A. Otherwise, a timeout may occur when pings from the PED fail to bedetected for a predetermined time interval and processing will againreturn to the slow ping mode to conserve power.

The presently described system, apparatus, and methods take advantage ofthe acquired frequency knowledge to allow for synthesis of a time andphase coherent response to accurately determine location with alow-power MT. Although the preceding description describes variousembodiments of the system, the invention is not limited to suchembodiments, but rather covers all modifications, alternatives, andequivalents that fall within the spirit and scope of the invention. Forexample, the positioning of the various components may be varied, thefunctions of multiple components can be combined, individual componentsmay be separated into different components, or components can besubstituted as understood in the art. Since many embodiments of theinvention can be made without departing from the spirit and scope of theinvention, the invention is not limited except as by the appendedclaims.

1. A method for determining the position of a transponder with a radiotransceiver in personal electronic devices that also each include asatellite navigation system, the method comprising: identifying a targetID associated with the transponder; sending a transponder locationrequest to each of the personal electronic devices; receiving a locationand distance measurement from each of the personal electronic devicesafter sending the transponder location request; and calculating alocation associated with the transponder from at least a portion of thereceived location and distance measurements by: determining a circle foreach received distance measurement at a geographic position associatedwith the corresponding received location; identifying a common pointarea that is created by an overlap of circles; and identifying thelocation and distance to the transponder based on the identified commonpoint area.
 2. The method of claim 1, wherein calculating the locationassociated with the transponder from at least a portion of the receivedlocation and distance measurements further comprises adjusting theradius of each circle according to a corresponding one of the receiveddistance measurements.
 3. The method of claim 1, further comprising:sending a message to a requesting personal electronic device with theidentified location and distance to the transponder, wherein a userinitiated the transponder position determination with the requestingpersonal electronic device.
 4. The method of claim 1, furthercomprising: sending a message to a personal computer device with theidentified location and distance to the transponder, wherein a userinitiated the transponder position determination with the personalcomputer device.
 5. The method of claim 1, wherein each identifiedpersonal electronic device is arranged for: receiving the transponderlocation request; executing a radio set configuration logic such thatthe radio transceiver is reconfigured from a cellular telephone mode toa locator mode, wherein the software defined radio transceiver isarranged for: selecting a target ID associated with the transponder fromthe transponder location request; coding a sequence for the selectedtarget ID; initiating the transmission of a structured multi-frametransmission to the transponder over a first time interval with thesoftware configured radio transceiver; identifying a geographic locationfor the personal electronic device with the satellite navigation systemwhen the transmission is initiated; capturing samples of a signalspectrum over a second time interval that is subsequent to the firsttime with the software configured radio transceiver; correlating thecaptured samples over a third time interval with the software configuredradio transceiver; detecting a valid reply from the transponder devicewhen the captured samples correlate to a structured reply transmissionfrom the transponder with a reply cadence and frequency thatsubstantially matches the expected reply cadence and frequency based onthe internal clock of the personal electronic device; and determining around-trip time-of-flight between the transmission of the structuremulti-frame transmission and the detected valid reply; calculating adistance measurement from the determined round-trip time-of-flight; andsending a message including the calculated distance measurement and theidentified geographic location.
 6. A system for determining the positionof a transponder with personal electronic devices, the methodcomprising: a transponder; a satellite navigation system; personalelectronic devices (PEDs) that each comprise a radio transceiver; acomputing device that is configured to identify a target ID associatedwith the transponder and send a transponder location request to thePEDs; wherein each of the PEDs is configured to perform operations,comprising: receive the transponder location request; determine alocation and distance measurement of the transponder; send the locationand distance measurement to the computing device; the computing deviceperforming actions, comprising: receiving the location and distancemeasurements from at least a portion of the PEDs; calculating a locationassociated with the transponder from at least a portion of the receivedlocation and distance measurements by: determining a circle for eachreceived distance measurement at a geographic position associated withthe corresponding received location; identifying a common point areathat is created by an overlap of circles; and identifying the locationand distance to the transponder based on the identified common pointarea.
 7. The system of claim 6, wherein calculating the locationassociated with the transponder from at least a portion of the receivedlocation and distance measurements further comprises adjusting theradius of each circle according to a corresponding one of the receiveddistance measurements.
 8. The system of claim 6, wherein the computingdevice is a PED.
 9. The system of claim 6, wherein the computing deviceis a server.
 10. The system of claim 6, wherein each of the PEDs isarranged for: executing a radio set configuration logic such that theradio transceiver is reconfigured from a cellular telephone mode to alocator mode, wherein the software defined radio transceiver is arrangedfor: selecting a target ID associated with the transponder from thetransponder location request; coding a sequence for the selected targetID; initiating the transmission of a structured multi-frame transmissionto the transponder over a first time interval with the softwareconfigured radio transceiver; identifying a geographic location for thepersonal electronic device with the satellite navigation system when thetransmission is initiated; capturing samples of a signal spectrum over asecond time interval that is subsequent to the first time with thesoftware configured radio transceiver; correlating the captured samplesover a third time interval with the software configured radiotransceiver; detecting a valid reply from the transponder device whenthe captured samples correlate to a structured reply transmission fromthe transponder with a reply cadence and frequency that substantiallymatches the expected reply cadence and frequency based on the internalclock of the personal electronic device; and determining a round-triptime-of-flight between the transmission of the structure multi-frametransmission and the detected valid reply; calculating a distancemeasurement from the determined round-trip time-of-flight; and sending amessage including the calculated distance measurement and the identifiedgeographic location.